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xgboost/cub/cub/block/specializations/block_scan_warp_scans3.cuh  view on Meta::CPAN

 * \file
 * cub::BlockScanWarpscans provides warpscan-based variants of parallel prefix scan across a CUDA threadblock.
 */

#pragma once

#include "../../util_arch.cuh"
#include "../../util_ptx.cuh"
#include "../../warp/warp_scan.cuh"
#include "../../util_namespace.cuh"

/// Optional outer namespace(s)
CUB_NS_PREFIX

/// CUB namespace
namespace cub {

/**
 * \brief BlockScanWarpScans provides warpscan-based variants of parallel prefix scan across a CUDA threadblock.
 */
template <
    typename    T,
    int         BLOCK_DIM_X,    ///< The thread block length in threads along the X dimension
    int         BLOCK_DIM_Y,    ///< The thread block length in threads along the Y dimension
    int         BLOCK_DIM_Z,    ///< The thread block length in threads along the Z dimension
    int         PTX_ARCH>       ///< The PTX compute capability for which to to specialize this collective
struct BlockScanWarpScans
{
    //---------------------------------------------------------------------
    // Types and constants
    //---------------------------------------------------------------------

    /// Constants
    enum
    {
        /// The thread block size in threads
        BLOCK_THREADS = BLOCK_DIM_X * BLOCK_DIM_Y * BLOCK_DIM_Z,

        /// Number of warp threads
        INNER_WARP_THREADS = CUB_WARP_THREADS(PTX_ARCH),
        OUTER_WARP_THREADS = BLOCK_THREADS / INNER_WARP_THREADS,

        /// Number of outer scan warps
        OUTER_WARPS = INNER_WARP_THREADS
    };

    ///  Outer WarpScan utility type
    typedef WarpScan<T, OUTER_WARP_THREADS, PTX_ARCH> OuterWarpScanT;

    ///  Inner WarpScan utility type
    typedef WarpScan<T, INNER_WARP_THREADS, PTX_ARCH> InnerWarpScanT;

    typedef typename OuterWarpScanT::TempStorage OuterScanArray[OUTER_WARPS];


    /// Shared memory storage layout type
    struct _TempStorage
    {
        union
        {
            Uninitialized<OuterScanArray>           outer_warp_scan;  ///< Buffer for warp-synchronous outer scans
            typename InnerWarpScanT::TempStorage    inner_warp_scan;  ///< Buffer for warp-synchronous inner scan
        };
        T                               warp_aggregates[OUTER_WARPS];
        T                               block_aggregate;                           ///< Shared prefix for the entire threadblock
    };


    /// Alias wrapper allowing storage to be unioned
    struct TempStorage : Uninitialized<_TempStorage> {};


    //---------------------------------------------------------------------
    // Per-thread fields
    //---------------------------------------------------------------------

    // Thread fields
    _TempStorage    &temp_storage;
    unsigned int    linear_tid;
    unsigned int    warp_id;
    unsigned int    lane_id;


    //---------------------------------------------------------------------
    // Constructors
    //---------------------------------------------------------------------

    /// Constructor
    __device__ __forceinline__ BlockScanWarpScans(
        TempStorage &temp_storage)
    :
        temp_storage(temp_storage.Alias()),
        linear_tid(RowMajorTid(BLOCK_DIM_X, BLOCK_DIM_Y, BLOCK_DIM_Z)),
        warp_id((OUTER_WARPS == 1) ? 0 : linear_tid / OUTER_WARP_THREADS),
        lane_id((OUTER_WARPS == 1) ? linear_tid : linear_tid % OUTER_WARP_THREADS)
    {}


    //---------------------------------------------------------------------
    // Exclusive scans
    //---------------------------------------------------------------------

    /// Computes an exclusive threadblock-wide prefix scan using the specified binary \p scan_op functor.  Each thread contributes one input element.  With no initial value, the output computed for <em>thread</em><sub>0</sub> is undefined.
    template <typename ScanOp>
    __device__ __forceinline__ void ExclusiveScan(
        T               input,                          ///< [in] Calling thread's input item
        T               &exclusive_output,              ///< [out] Calling thread's output item (may be aliased to \p input)
        ScanOp          scan_op)                        ///< [in] Binary scan operator
    {
        // Compute block-wide exclusive scan.  The exclusive output from tid0 is invalid.
        T block_aggregate;
        ExclusiveScan(input, exclusive_output, scan_op, block_aggregate);
    }


    /// Computes an exclusive threadblock-wide prefix scan using the specified binary \p scan_op functor.  Each thread contributes one input element.
    template <typename ScanOp>
    __device__ __forceinline__ void ExclusiveScan(
        T               input,              ///< [in] Calling thread's input items
        T               &exclusive_output,  ///< [out] Calling thread's output items (may be aliased to \p input)
        const T         &initial_value,     ///< [in] Initial value to seed the exclusive scan
        ScanOp          scan_op)            ///< [in] Binary scan operator